Effect of grazing and cultivation on some chemical properties of soils in the mixed prairie

Abstract

Components of the organic matter were studied in soil under 3 Mixed Prarie types: grassland dominated by needle-and-thread/blue grama (Stipa comata Trin. and Rupr./Bouteloua gracilis (HBK.) Lag. ex Steud.) in good range condition; grassland significantly modified by grazing, dominated by blue grama and in poor range condition; and grassland, dominated by needle-and-thread/blue grama in good range condition, but converted to cropland and under continuous wheat for 4 years. The soils were sampled on 13 April 1988. Concentrations of total organic carbon in the upper 2 cm were 1.39, 2.70, and 1.87%, respectively. The higher organic carbon under blue grama was caused by an active, ramified, fine rootmass which gave rise to most of the monosaccharides being of microbial origin. The monosaccharides in the lower Ap horizon in the cropland were generally of plant origin from incorporated straw. The Ah horizons of the needle-and-thread/blue grama and blue grama sites and the Ap horizon of the cultivated site yielded 244, 696, and 370 migrograms g-1 organic acids in the alkaline-soluble fraction of the soil, respectively. Although most of the organic compounds identified were present in all 3 soils, the quantitative patterns were quite different. Differences exist due to inputs by different species, and 4 years of cropping also made significant soil chemical changes. This study demonstrated the importance of recognizing the history of the soils studied when describing soil quality.